xvin THE CLASSIFICATION OF THE ELEMENTS 481 



This view was supported by tables showing the actual 

 densities of various gases relatively to hydrogen, and the 

 hypothetical densities of many solid elements and com- 

 pounds ; from these the " specific gravities " or equivalents 

 of the elements were deduced as a series of integral 

 numbers, thus : 



H C N P O S Ca Na Fe Zn Cl K Ba I 

 i 6 14 14 16 16 20 24 28 32 36 40 70 124 



Hypothetical values for 23 other elements were all shown 

 as multiples of 4. 



Prout on the specific gravity of hydrogen (1815). 

 Whilst the idea that all the atomic weights are even 

 multiples of the atomic weight of hydrogen is obviously 

 untrue, credit must be given to Prout for determining for 

 the first time the correct density of hydrogen, by an indirect 

 method, as follows : 



" The specific gravity of hydrogen, on account of its 

 great levity, and the obstinacy with which it retains water, 

 has always been considered as the most difficult to take of 

 any other gas. ... It occurred to me that its specific 

 gravity might be much more accurately obtained by calcu- 

 lation from the specific gravity of a denser compound into 

 which it entered in a known proportion. Ammoniacal gas 

 appeared to be the best suited to my purpose, as its specific 

 gravity had been taken with great care by Sir H. Davy, and 

 the chance of error had been much diminished from the 

 slight difference between its specific gravity and that of 

 steam. . . . The specific gravity of ammonia, according 

 to Sir H. Davy, is '590164, atmospheric air being 1*000. 

 We shall consider it as '5902. . . . Now ammonia consists 

 of three volumes of hydrogen and one volume of azote 

 condensed to two volumes. Hence the specific gravity of 

 hydrogen will be found to be '0694, 1 atmospheric air being 

 i -oooo. It will be also observed that the specific gravity of 



1 " Let * = sp. gr. of hydrogen, then 3* +'9722 = . 59O2 . 

 Hence *= ri8o 4-'97 22 = -o6 9 4." 



I I 



